This invention relates to an electronic circuit for use with an electrical generator having a speed governor which responds to raise or lower control signals to change the generator output frequency and phase to approach the frequency and phase of a bus to which the generator will be synchronized.
When an electrical generator is connected to an energized electrical system, the generator voltage parameters, such as magnitude, frequency and phase angle must be matched to the parameter of the electrical system. Electrical apparatus are presently available which will accomplish this matching prior to closing the generator breaker. However, the time required to match the generator voltage to the electrical system voltage (e.g., parameter bus voltage, frequency and phase angle) is very often excessive.
For example, some presently available circuits will provide a continuous raise or lower signal until the difference between the generator frequency and bus frequency is adjusted to within permissible limits. If a continuous raise signal was being applied (i.e., the generator frequency was too low), the generator frequency may overshoot the desired value and hunt for some time before a frequency match is attained.
Some frequency matching systems have attempted to solve this overshooting and hunting problem by periodically providing raise or lower control signals which are pulses. For example, the pulses will have a presettable pulse width or duration produced when the frequency difference is above a predetermined threshold. When the frequency difference is below this predetermined threshold, correction pulses will cease. Thus, below this latter predetermined threshold, the generator frequency is not controlled.
Synchronizers which control voltage are well known, such as disclosed in co-assigned U.S. Pat. No. 4,800,291 issued Jan. 24, 1989 for "Electronic Circuit for Control of a Voltage Regulator of an Electrical Generator," the entire disclosure of which is incorporated herein by reference. There is a need for a synchronizer which controls frequency (speed) in addition to voltage so that the generator output voltage, the generator output frequency, and the generator output phase approach the voltage, frequency and phase of the bus to which the generator will be synchronized.